The purpose of this research is to determine the role of direct effects of hyperthermia on mitochondria in the process of heat-induced cytotoxicity. Relationships between cellular "thermal tolerance" and heat induced protective effects on mitochondrial function will also be investigated. Studies will include investigation of changes in respiratory function in heated cells, in mitochondria isolated from heated cells, and in heated mitochondria. Assays will include oxigen consumption, energy charge, Rhodamine 123 fluorescence as measured by flow cytometry, and cell survival. Both immediate and delayed effects will be measured. The role of mitochondria in the process of thermal tolerance will also be investigated. Determination of relationship between protection provided to mitochondria and cellular thermal tolerance will be studied. Thermal protection of isolated mitochondria by subcellular components and specific compounds which may be associated with thermal tolerance will also be investigated. Cellular respiratory state undoubtedly plays an important role in determining sensitivity of tumors ot clinical hyperthermia treatments. This investigation should provide information which will enhance the efficancy of such therapeutic use of hyperthermia. Knowledge about the relationship between respiratory state prior to heat treatment and thermal sensitivity may allow more accurate prognoses in hyperthermia therapy. Furthermore, an understanding of respiratory changes after heat exposure will allow better application of fractionated heat treatments and due to oxygen concentration effects, better application of heat-radiation combinations.